1. Field of the Invention
The present invention relates to an electric motor for sealed compressors. More specifically, the invention relates to technology for maintaining insulation of conductor ends of a stator coil and other free conductors in an electric motor for sealed compressors that use a fluorine-contained coolant and further use, as a refrigerator oil, a polyalkylene glycol oil, a polyol ester oil or a polyvinyl ether oil.
2. Description of the Related Art
The present applicant has previously developed an alternator featuring a compact size, a high output and low noise, and disclosed it as Japanese Patent No. 2927288. This alternator is equipped with a stator of a constitution in which a coil wound on the stator core is constituted by a plurality of conductor segments, and the ends (coil ends) of the conductor segments protruding beyond the core are joined to each other to form a coil. This alternator is the one used for the vehicles, assures a high output required for the alternators for vehicles by providing the structure of a rotor and a stator winding capable of producing the output from a low-speed region and, by providing a novel constitution for cooling the coil ends of the stator winding, suppressing a reduction in the efficiency and output caused by the generation of heat. The alternator for vehicles further features improved space factor in the slots of the stator winding while increasing the cooling ability and reducing noise on the outside of the slots as a result of cooperation with the rotor. The alternator for vehicles further suppresses a local temperature rise in the stator winding and suppresses the occurrence of magnetic noise.
The present invention is concerned with solving problems that arouse when the above alternator of the novel structure is applied and, particularly, when the structure of the stator is applied to an electric motor for wholly sealed compressors.
That is, the present applicant has developed an electric motor for wholly sealed compressors, featuring a compact size, a high output and low noise by applying the structure of the stator of the above alternator to the electric motor for wholly sealed compressors that use, as a coolant, a fluorinated hydrocarbon (HFC) such as 1,1,1,2-tetrafluoroethane.
However, it has been known that the insulating material tends to be easily deteriorated as the wholly sealed compressor uses a fluorinated hydrocarbon (HFC) such as 1,1,1,2-tetrafluoroethane as a coolant and further uses a polyalkylene glycol oil or a polyol ester oil as a refrigerator oil. To solve this problem, Japanese Unexamined Patent Publication (Kokai) No. 5-236693 discloses the use of 1,1,1,2-tetrafluoroethane as a coolant, polyalkylene glycol oil or polyol ester oil as a refrigerator oil, polyethylene terephthalate as an insulating film and polyester varnish as a conductor insulating layer. According to the above publication, it is possible to maintain the life longer than that of the electric motor for wholly sealed compressors that have heretofore been stably used by employing the above constitution even when the fluorinated hydrocarbon (HFC) such as 1,1,1,2-tetrafluoroethane is used as a coolant, and the polyalkylene glycol oil or the polyol ester oil is used as the refrigerator oil.
The inventors, however, have encountered the following problems when they have attempted to fabricate an electric motor for wholly sealed compressors of the invention according to the disclosure of Japanese Unexamined Patent Publication (Kokai) No. 5-236693.
In the electric motor for wholly sealed compressors, a stator core has a laminated core forming a plurality of slots extending through a laminated plate, a multi-phase stator winding has a plurality of conductor segments which are held in the slots being insulated from each other and are arranged extending toward the end surface side of the stator core outside the slots, coil ends are formed by connection patterns that connect in series different layers in the slots spaced apart to meet a pitch of magnetic poles of the rotor thereby to form a group of coil ends repeating chiefly the connection pattern on the end surface side of the stator core, the coil ends being spaced apart from each other. In the electric motor for wholly sealed compressors, the stator coil ends are spaced apart from each other and are insulated. Therefore, no insulating layer is necessarily required. However, a polyester varnish is applied as an insulating layer to the conductors in general of the motor for wholly sealed compressors inclusive of the coil ends.
However, the polyester varnish chiefly comprises liquid components and has no force for firmly holding the positions of the conductors. Prior to being mounted in the compressor after the varnish has been applied to the stator, therefore, the free conductor portions are subject to be deformed being caused by violent handling by the worker or due to shocks during the transit. As a result, the conductors often come into frictional contact giving rise to the occurrence of defective insulation. In the electric motor for wholly sealed compressors, in particular, the coil ends of the stator are freely protruding and are subject to be deformed to cause defective insulation. Shocks similar to those of during the transit may occur even after the products have been completed.